The present disclosure generally relates to subterranean treatment operations and, more specifically, to treatment fluids and methods for inhibiting precipitation and/or corrosion.
Treatment fluids can be used in a variety of subterranean treatment operations. Such treatment operations can include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, sand control treatments, and the like. As used herein, the terms “treat,” “treatment,” “treating,” and grammatical equivalents thereof will refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component thereof, unless otherwise specified herein. More specific examples of illustrative treatment operations can include drilling operations, fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal operations, sand control operations, consolidation operations, and the like.
Downhole acidizing operations and like dissolution processes (e.g., descaling and damage removal operations) may be used to stimulate a subterranean formation for increasing production of a hydrocarbon resource therefrom. During an acidizing operation or a like dissolution process, an acid-soluble material in the subterranean formation may be dissolved by one or more acids to expand existing flow pathways in the subterranean formation, to create new flow pathways in the subterranean formation, and/or to remove acid-soluble precipitation damage in the subterranean formation, thereby stimulating the formation's production capabilities. Introduction of an acidizing fluid to a subterranean formation may take place at matrix flow rates without fracturing of the formation matrix or at higher injection rates and pressures to fracture the formation, the latter being commonly referred to as an acid-fracturing operation. The acid-soluble material being dissolved by the acid(s) may be part of or formed from the native formation matrix or may have been deliberately introduced into the subterranean formation in conjunction with a treatment operation (e.g., bridging agents, proppants, or gravel particulates). Illustrative substances within the native formation matrix that may be dissolved by an acid include, but are not limited to, carbonates, silicates and aluminosilicates, which may be present alone or in combination with one another in formations of mixed mineralogy. Other substances may also be dissolved during the course of performing an acidizing operation or like dissolution process, and the foregoing substances should not be considered to limit the scope of substances that may undergo dissolution. The acids used during such dissolution processes may also be corrosive toward various types of metal surfaces (e.g., pipelines, tubulars and other downhole metal goods), and numerous corrosion inhibitors have been developed to lessen the severity of corrosion.
Carbonate formations can contain minerals that comprise a carbonate anion (e.g., calcite (calcium carbonate), dolomite (calcium magnesium carbonate), siderite (iron carbonate) and like minerals). When acidizing a carbonate formation, acidity of the treatment fluid alone may often be sufficient to solubilize a carbonate material by decomposing the carbonate anion to carbon dioxide and leeching a metal ion into the treatment fluid. Both mineral acids and organic acids may be used to treat a carbonate formation in this respect, often with similar degrees of success. Since it is relatively inexpensive, hydrochloric acid is very commonly used, typically in concentrations up to about 28% by volume. Other mineral acids and organic acids may be commonly used as well.
Siliceous formations can contain minerals such as, for example, zeolites, clays, feldspars and sandstone. As used herein, the term “siliceous” will refer to a substance having the characteristics of silica, including silicates and/or aluminosilicates. The acids that can effectively dissolve carbonate materials may have little effect on siliceous materials. Hydrofluoric acid, however, can react very readily with siliceous materials to promote their dissolution. Oftentimes, a secondary mineral acid or an organic acid can be used in conjunction with hydrofluoric acid to maintain a low pH state as the hydrofluoric acid becomes spent during dissolution of a siliceous material, where the low pH state helps promote continued solubilization of the siliceous material. Many types of siliceous formations can also contain varying amounts of carbonate materials. Most sandstone formations, for example, contain about 40% to about 98% sand quartz particles (i.e., silica) that are bonded together by various amounts of cementing materials, which may be siliceous in nature (e.g., aluminosilicates or other silicates) or non-siliceous in nature (e.g., carbonates, such as calcite). When siliceous materials are co-present with carbonate materials, significant precipitation issues can frequently be encountered due to interaction of dissolved metal ions from the carbonate material with fluoride ions from the hydrofluoric acid. For example, calcium ions liberated from a carbonate material can react readily with fluoride ions to form highly insoluble calcium fluoride, which can lead to extensive damage within a subterranean formation. Other metal ions, such as aluminum, can also be problematic in this regard. During sandstone acidizing, for example, aluminum scale and calcium fluoride precipitation issues can be very problematic.
One approach that can be used to address the presence of metal ions in a subterranean formation is to employ chelating agents that effectively sequester any problematic metal ions in a metal-ligand complex once the metal ions have been liberated from their source. As used herein, the terms “complex,” “complexing,” “complexation” and other variants thereof will refer to the formation of a metal-ligand bond without reference to the mode of bonding. Although complexation of a metal ion may involve a chelation process in some embodiments, complexation is not deemed to be limited in this manner. Once bound in a metal-ligand complex, the problematic metal ions may be substantially unable to undergo a further reaction to form damaging metal-containing precipitates. Although precipitation can be a particular concern when acidizing a siliceous material, chelating agents may also be used with similar benefits in conjunction with acidizing subterranean formations that comprise substantially only a carbonate material. In addition to sequestering previously liberated metal ions, chelating agents may also be used to affect direct dissolution of a metal ion from a carbonate material, even without another acid being present.
Dissolved silicon compounds from siliceous formations can also be very problematic, both by themselves and in the presence of metal ions. Alkali metal ions, for example, in the presence of dissolved silicon compounds can lead to formation of highly insoluble alkali metal fluorosilicates. Metal ions such as aluminum can also lead to vigorous re-precipitation of previously dissolved silicon compounds. Although dissolved silicon compounds can initially be soluble at low pH values during an acidizing operation or like dissolution process, the solubility limit may be quickly exceeded as the acid spends and the pH rises, thereby leading to re-precipitation of various silicon species even in the absence of dissolved metal ions. The re-precipitated silicon species may be in a variety of forms such as, for example, amorphous silica, silica gels, colloidal silica and/or hardened silica scales. In some instances, re-precipitation of previously dissolved silicon compounds can be even more damaging to a subterranean formation than if an acidizing operation or like dissolution process had not been performed in the first place.
To combat the detrimental effects resulting from re-precipitation of dissolved silicon compounds, a number of silica scale control additives have been identified. As used herein, the term “silica scale control additive” will refer to a substance that limits deposition of amorphous, gelatinous and/or colloidal silica that leads to silica scale buildup. Illustrative silica scale control additives that have been used in this regard include, but are not limited to, polyaminoamide dendrimers, polyethyleneimine, carboxymethylinulin, polyacrylates, phosphonates, aminocarboxylic acids, polyaminocarboxylic acids and ortho-dihydroxybenzene compounds related to tannic acid.